As early as 1988, Henkel Corporation began marketing a line of methylated fatty acids, and more specifically, methylated soybean oil, as a replacement for commonly used organic solvents used in pesticide formulations. These methyl esters were and still are, promoted as being safer solvents because of their high flash point, relative to more commonly used aromatic hydrocarbons. In 1986, F. A. Manthey, et. Al., published a paper showing their work on various alkylated esters of different natural oils (soybean and sunflower). This work demonstrated that alkylated esters of soybean oil and sunflower oil can enhance the uptake of oxime herbicides (commonly referred to as "dims" or graminicides, i.e. sethoxydim, clopropoxydim.), and 2-(4-aryloxyphenoxy)alkanoic acid herbicides (commonly known as "fops", i.e. diclofop, quizalofop, fluazifop). In 1989, Hazen, et.al. demonstrated the effectiveness of a methylated sunflower oil adjuvant on the uptake of sethoxydim. Furthermore, it was reported that methylated sunflower oil could actually increase the stability of sethoxydim in direct sunlight. Also in 1989, Manthey, et.al. reported that alkylated vegetable oils such as soybean oil and sunflower oil, could increase the realtive wax solubility of pesticide sprays. In 1991, more work was done by Urvoy, et Al. That demonstrated the effectiveness of alkylated fatty acids in enhancing the uptake of gramincides. In 1993, Serre, et.al. reported that alkyl esters of oleic acid could enhance the efficacy of quizalofop-ethyl, a 2-(4-aryloxyphenoxy)alkanoic acid herbicide, and phenmedipham, a bis-carbamate herbicide. In 1995, McMullan, et.al. demonstrated the effectiveness of methylated fatty acids in enhancing the efficacy of tralkoxydim, another graminicide herbicide.
Chlorinated phenoxy acid compounds comprise a family of herbicides that are used in the form of their parent acids, and more commonly as their salts and esters. The most common member of this herbicide family is 2,4-D [(2,4-dichlorophenoxy)acetic acid]. Two other commonly used compounds in this family are 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] and MCPA[[(4-chloro-o-tolyl)oxy]acetic acid]. Additional herbicides in this family are 2,4-DB [4(2,4-dichlorophenoxy)butyric acid], MCPB [4-[(4-chloro-o-tolyl)oxy]butyric acid], silvex [2-(2,4,5-trichorophenoxy)propionic acid], dichlorprop [2-(2,4-dichlorophenoxy)propionic acid], mercoprop [2-[(4-chloro-o-tolyl)oxy]propionic acid]. These herbicides are plant growth regulator compounds with hormone-like activity.
The ester forms of these compounds are represented by the alkyl esters (mainly methyl, isopropyl, butyl, and octyl) and the low-volatile esters (butoxyethanol, propyleneglycolbutylether, and iso-octyl).
The major controllable factors of chlorinated phenoxy herbicides have been reported by Ashton and Crafts as being pH, concentration, and additives (i.e. surfactants). Absorption of chlorinated phenoxy herbicides is reported to be optimal at low pH ranges. While surfactants have been reported to enhance the activity of chlorinated phenoxy herbicides in some instances, no one surfactant could be selected which consistently enhanced the uptake of the herbicide. The authors cite work done by Bukovac in 1976 showing that foliar penetration is generally linearly related to the external herbicide concentration.
Recently, the family of 2,4-D herbicides has come under regulatory scrutiny due to the potential of spray mixes to drift to off-target areas. This drift is caused by volatilization of both sprays and of spray deposits. Therefore, it would be beneficial if the per acre use rate of these compounds could be reduced, thereby affording a reduction in driftable herbicide. Any attempt to reduce herbicide drift, however, must not demonstrate a reduction in herbicide efficacy.